Gammarus setosus
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| Gammarus setosus Dementieva, 1931 |
Gammarus setosus is a small invertebrate, approximately 1 cm in length. Its green-grey body is segmented with several jointed appendages and two larger antennae near the head (Campbell and Reece 2001). As with all members of the Malacostraca, Gammarus setosus has mouthparts located at the head segments, with their legs branching from each thoracic section, and most of their abdominal sections (Steele and Steele 1970). Typically, Gammarus setosus is found in the benthic sub-tidal or low inter-tidal regions. They can be found in the waters off the coast of British Columbia, but have been observed in nearly all of the world's oceans (Chavanich and Wilson 2000). This insect is extremely important in the development of freshwater fish trout and is particularly important for fly fishing.
It has been documented that the different species of gammaridean amphipods tend to accumulate in zones corresponding to the abundance of the algae that they eat. In a study involving the inter-tidal distribution of such organisms, it was found that Gammarus species were more likely to be located in areas where one of their important food sources, Chondrus crispus was prevalent (Chavanich and Wilson 2000). In addition to algae, Gammarus setosus often consumes animal material that has settled to the sea floor. There have been a few cases in which Gammarus species have preyed upon other small, weak or stressed marine organisms (Newman 2005). However, due to their primarily scavenging nature, they are identified as detritivores and serve a crucial role in the diet of other invertebrates, fish and even some whales (Wisenden et al. 1999). Occasionally they are eaten by terrestrial organisms, namely shorebirds and insects that dwell near the ocean (Wudkevich et al. 1997).
Reproduction occurs through a process in which the male carries the female on his back for a length of time, often up to a week. Gammarus setosus may reproduce many times in a year, which is often the length of their lifespan, generating up to 100 young per episode (Newman 2005). Relative success of growth and reproduction has been shown to correspond to the length of the photoperiod in a given habitat. Gammarus setosus can survive in most intensities of light that will occur in their natural environment but are more active at night (FOSSweb 2004) or in the darker, lower light intensity of the sea floor (Steele and Steele 1986). At temperatures above 20°C, reproduction and growth are greatly accelerated and lifespan becomes significantly shorter (Neuparth et al. 2002). Ideally, Gammarus setosus lives in water around 15°C but can survive in temperatures approximately 10°C above or below this value (Kruschwitz 1978).
Salinity is a less important factor, as it has a greater tolerable range and will not vary as much in a given environment. A salinity of 33 ppt is ideal; however, at times Gammarus setosus are caught in tide pools, where they must survive in water that can reach upwards of 40 ppt (Chavanich and Wilson 2000). On the other end of the spectrum, survival is possible in salinity as low as 10 ppt (Kruschwitz 1978). In fact, some Gammarus species thrive in the very low salinity of fresh water lakes (Newman 2005).
Although not as vital to reproduction or growth, currents in the water column are very important for movement. Floating comprises the primary mode of locomotion, yet they can also swim in short, concentrated bursts. Descriptive of their body orientation while manoeuvring themselves, Gammarus are often referred to as side-swimmers (FOSSweb 2004).
[edit] References
- Campbell, N.A., and Reece, J.B. 2001. Biology Sixth Edition. Pearson Education, Inc., Benjamin Cummings, San Francisco, CA.
- Chavanich, S., and Wilson, K.A. 2000. Rocky intertidal zonation of Gammaridean Amphipods in Long Island Sound, Connecticut. Crustaceana, 73(7):835-846.
- FOSS project. GAMMARUS. 2004. A general description of Gammarus [online]. Available from http://www.lawrencehallofscience.org/foss/fossweb/teachers/materials/plantanimal/gammarus.html [cited 23 October 2005].
- Kruschwitz, L.G. 1978. Environmental factors controlling reproduction of the amphipod Hyalellia azteca. Proceedings of the Oklahoma Academy of Science, 58:16-21.
- Neuparth, T., Costa, F.O., and Costa, M.H. 2002. Effects of temperature and salinity on life history of the marine amphipod Gammarus locusta. Implications for ecotoxicological testing. Ecotoxicology, 11(1):61-73.
- Newman, R. Freshwater shrimp. A general description of Gammarus shrimp [online]. Available from http://www.bcadventure.com/adventure/angling/bugs/shrimp/shrimp.phtml [cited 23 October 2005].
- Steele, V.J., and Steele, D.H. 1970. Biology of Gammarus (Crustacea, Amphipoda) in Northwestern Atlantic. Canadian Journal of Zoology, 48(4):659.
- Steele, V.J., and Steele, D.H. 1986. The influence of photoperiod on the timing of reproductive cycles in Gammarus species (Crustacea, Amphipoda). American Zoologist, 26(2):459-467.
- Wisenden, B.D., Cline, A., and Sparkes, T.C. 1999. Survival Benefit to Antipredator Behavior in the Amphipod Gammarus minus (Crustacea: Amphipoda) in Response to Injury-released Chemical Cues from Conspecifics and Heterospecifics. Ethology, 105:407-414.
- Wudkevich, K., Wisenden, B.D., Chivers, D.P., and Smith, J.F. 1997. Reactions of Gammarus lacustris to chemical stimuli from natural predators and injured conspecifics. Journal of Chemical Ecology, 23:1163-1172.
